Production of hollow acrylic fibers

ABSTRACT

PROCESS FOR PRODUCING HOLLOW ACRYLIC SYNTHETIC FIBERS BY EXTRUDING A SPINNING SOLUTION OF AN ACRYLIC POLYMER AND A CONCENTRATED AQUEOUS SOLUTION OF AN INORGANIC SALT THROUGH SPINNING ORIFICES INTO AN INERT GASEOUS MEDIUM WHICH IS INCAPABLE OF COAGULATING THE SPINNING SOLUTION, EACH SPINNING ORIFICE HAVING A CONTINUOUS CENTRAL PORTION SUBSTANTIALLY ENCLOSED BY A SLIT (SEE FIGURES) AND COAGULATING THE THUS-FORMED HOLLOW CURRENT OF THE SPINNING SOLUTION WITHIN WHICH IS ENCLOSED THE INERT GAS.

Aug. 17, 1971 rr o sHlMODA ETAL 3 ,600,491

PRODUCTION OF HOLLOW ACRYLIC FIBERS F'ile d Jan. 28, 1969 2 Sheets-Sheet1 FIG] F|G.2 F|G.3

F|G.4 |G.5 F|G.6

a 2 f 2 2 I I 3 KEITARO SHIMODA and KEITARO FUKUSIIIMA,

Inventor s By, 1W

cl Attorney 5 Aug. 17, 1971 KElTARQ SHIMQDA EI'AL 3,600,491

PRODUCTION OF HOLLOW ACRYLIC FIBERS 2 Sheets-Sheet 2 Filed Jan. 28, 1969FIG.

KEITARO SHIMODA and KEITARO FUKUSHIMA,

lnvenlor s ywMdflj/w MJWM, Atlorney s United States Patent 3,600,491PRUDUCTKON F HQLLUW ACRYLJC FIBERS Keitaro Shimoda and KeitaroPukushima, Saidaiji, Japan, assignors to Japan Exlan Company LimitedFiled Jan. 28, 1969, Ser. No. 794,696 Claims priority, applicationJapan, Feb. 14, 1968, 43/9527 lint. Cl. B2811 21/54; Dtlld 7/00 US. Cl.264ll77F 5 Claims ABSTRACT OF THE DlSCLOSURE This invention relates to aprocess for producing hollow acrylic fibers.

More particularly the present invention relates to a process forproducing hollow acrylic synthetic fibers characterized by extruding aspinning solution prepared by dissolving an acrylic polymer in aconcentrated aqueous solution of an inorganic salt into an inert gaseousmedium which does not coaguate the spinning solution through spinningorifices each having a continuous central part substantially enclosed byslit having at least one narrow cut-out so that, during the passagethrough the inert gaseous medium, there is formed a hollow current ofthe spinning solution within which is enclosed the inert gas, and thenleading the same into an aqueous coagulating bath so as to formcoagulated hollow filarnents.

There are already known many processes for producing hollow fibers. Forexample, according to Japanese patent publication No. 2,928/1967, thereis mentioned a process for producing hollow fibers by inserting anextremely fine tube into an orifice so that the delivery orifice is of aconcentric double tube type and feeding a gas through the said fine tubewhen a spinning solution is extruded through the annular orifice slit.However, the structure is very complicated and further, in the case of awet spinning process, the diameter of the orifice is so small that itwill be almost impossible to make such device as is mentioned above.

Further, according to US. Pat. No. 3,323,168, US. Pat. No. 3,340,571 orBritish Pat. N0. 853,062, there is mentioned a process for producinghollow fibers by a melt-spinning process or dry spinning process byusing a spinnerette having spinning orifices each consisting of anarcuate or spiral slit. However, this method is not applicable toconventional Wet spinning process and hollow fibers are not obtainablethereby.

We have made extensive researches and experiments to effectively producehollow acrylic fibers from a spinning solution prepared by dissolving anacrylic polymer in a solvent consisting of a concentrated aqueoussolution of an inorganic salt, and have accomplished the presentinvention.

A principal object of the present invention is to easily and effectivelyobtain hollow acrylic fibers by wet spinning process.

Another object of the present invention is to obtain hollow acrylicsynthetic fibers light in weight and having an excellent heat insulatingproperty.

A further object of the present invention is to obtain hollow acrylicsynthetic fibers having an excellent luster.

Other objects of the present invention will become clear from thefollowing description of the present invention.

The objects of the present invention can be attained by extruding aspinning solution prepared by dissolving an acrylonitrile polymer in aconcentrated aqueous solution of an inorganic salt into an inert gaseousmedium through spinning orifices each having a continuous central partsubstantially enclosed by a slit having at least one cut-out so that,during the passage through the inert gaseous medium, there is formed ahollow current of the spinning solution within which is enclosed theinert gas, and then passing the same through an aqueous coagulating bathso as to form coagulated hollow filaments.

The invention will be explained in more detail by referring to theaccompanying drawings wherein each of FIGS. 1-7 is an enlarged view ofan example of a spinning orifice which may be used in this invention,and each of FIGS. 8-10 is an enlarged photograph of a crosssection offilaments obtained by the process of this invention.

In carrying out the process of this invention an acrylic polymer havingan intrinsic viscosity (7 in dimethyl formamide at 30 C. of from 0.4 to4.0 is used. In case the intrinsic viscosity (v7) is higher than 4.0,the spinnability will be remarkably reduced and the obtained hollowacrylic synthetic fibers will be very brittle, while when the intrinsicviscosity (1 is lower than 0.4, hollow acrylic synthetic fibers having adesired strength required for clothes will not be obtained.

The viscosity of the spinning solution to be used in the process of thepresent invention is in the range of 4x10 to 10' centipoises, preferably5 10 to 2 10 centipoises at 30 C. For example, in the case of using aconcentrated aqueous solution of a thiocyanate as a solvent, suchpreferable viscosity can be attained by dissolving 17 to 35% by weightof an acrylic polymer in a concentrated aqueous solution of athiocyanate having a concentration of 47 to by weight. When theviscosity of the spinning solution at 30 C. is lower than 4x10centipoises, it will be difiicult to obtain hollow acrylic syntheticfibers. Further, in case the viscosity of the spinning solution at 30 C.is higher than 10 centipoises, the spinning solution current extrudedthrough the spinning slit will be difificult to join longitudinallyalong the entire length to form a complete hollow shape before itreaches the surface of the coagulating bath and therefore no hollowacrylic synthetic fiber will be obtained.

Generally, when the viscosity of the spinning solution is low, a hollowfiber having a substantially circular crosssection will be obtainedirrespective of the shape of the spinning orifice. As the viscosity ofthe spinning solution is increased, it will become possible to obtain ahollow fiber having a cross-section of a shape closer to that of thespinning orifice. Therefore, if the viscosity of the spinning solutionis made high and if the shape of the slit forming the spinning orificeis properly selected, it will be possible to obtain a hollow fiberhaving a noncircular cross-section.

The distance between the surface of the spinnerette and the surface ofthe solution in the coagulating bath is generally 0.2 to 5.0 cm.,preferably 0.2 to 2.0 cm. If the said distance is less than 0.2 cm., theslight rocking of the co agulating bath or the spinnerette will wet thesurface of the spinnerette with the coagulating solution and willadversely affect the spinnability, while if the said distance betweenthe surface of the spinnerette and the surface of the solution is madelonger than 5 cm., it will be difiicult to obtain hollow fibers.

The space between the spinnerette and coagulating bath should be filledwith an inert gas which does not coagulate the spinning solution. Mosttypically and usually, air is used as the inert gaseous medium. However,if desired any other gas which does not coagulate the spinning solutionmay also be used.

The spinning solution is extruded through the spinning orifices into theinert gaseous medium and then introduced into the coagulating bath.

As explained before, each of the spinning orifice or hole has a centralcontinuous portion surrounded by a slit having at least one narrowcut-out. Some examples of the spinning orifice which may be used in theinvention are shown in FIGS. 1-7 wherein the central continuous portion1 is surrounded by a slit 2 which has at least one narrow cut-out 3. Theslit may be curved or straight as shown. Of course the shape of thespinning orifice is not limited to those shown and any other shape maybe employed so far as it enables the formation of an inert gas filledhollow current of the spinning solution during the passage through thespace between the spinnerette and coagulating bath.

'It is preferable that the area of the continuous portion 1 surroundedby the slit 2 is at least 0.04 mm. If the area is smaller than 0.04 mm.it will be difficult to form satisfactory hollow fibers. The width d ofthe cutout 3 may vary depending on the particular shape of the spinningslit and also on the viscosity of the spinning solution. It ispreferable however that the width d is from 0.03 to 0.3 mm.

When the spinning solution is extruded through a spinning orifice asmentioned above there will be initially formed a hollow current of thespinning solution with a longitudinal side slit formed due to thecut-out 3. From this longitudinal side slit the ambient inert gas flowsinto the hollow space. During the further flow downward but prior toreaching the coagulating bath the said longitudinal side slit isself-closed to form an inert-gas filled hollow current of the spinningsolution, which is then introduced into the coagulating bath.

In this invention the acrylic polymers to be used are not onlypolyacrylonitrile but also acrylonitrile copolymers which contain atleast 70% by weight of acrylonitrile and also include a blend of two ormore of these polymers. Comonomers to be copolymerized withacrylonitrile to form the copolymers include methyl acrylate, ethylacrylate, butyl acrylate, octyl acrylate, methoxyethyl acrylate, phenylacrylate, cyclohexyl acrylate, dimethylaminoethyl acrylate andcorresponding methacrylates; alkyl substituted products and nitrogensubstituted products of acrylamides and methacrylamides; unsaturatedketones such as methyl vinyl ketone, phenyl vinyl ketone, methylisopropenyl ketone, etc.; vinyl carboxylates such as vinyl formate,vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, etc.;esters of ethylene alpha and beta carboxylic acids such as fumaric acid,citraconic acid, mesaconic acid, aconic acid, etc.; N-alkylmaleinimide;N-vinyl carbazol; N-vinyl sucoinimide; N-vinyl phthalimide; vinylethers; N-methylolacrylamide; vinyl pyridines such as 2-vinyl pyridine,4-vinyl pyridine and 2- methyl-5-vinyl pyridine; styrene and its alkylsubstituted products; allyl alcohol; vinyl chloride; vinylidenechloride; vinylidene cyanides; unsaturated organic sulfonic acids suchas allyl sulfonic acid, methalyl sulfonic acid, allyloxyethyl sulfonicacid, methallyloxyethyl sulfonic acid, allythioethyl sulfonic acid,allylthiopropanol sulfonic acid, isopropenylbenzene sulfonic acid, vinylbromobenzene sulfonic acid, vinyl fiuorobenzene sulfonic acid, styrenesulfonic acid, methyl styrene sulfonic acid, etc. and their watersoluble salts.

As for the concentrated aqueous solution of an inorganic salt to be usedas solvent for the polymers, there can be enumerated concentratedaqueous solutions of such thiocyanates as sodium thiocyanate, potassiumthiocyanate, ammonium thiocyanate and calcium thiocyanate,

4 such perchlorates as sodium perchlorate and calcium perchlorate andsuch inorganic salts as zinc chloride and lithium chloride.

For the coagulating bath may be used water or an aqueous solution ofsuch inorganic salt as is mentioned above having a concentration of lessthan Since these polymer solvents and coagulants are well known in theart of wet spinning of acrylic polymers no further detailed explanationwill be necessary.

The fibers spun by the process of the present invention may be washedwith water, stretched, dried and heattreated in the same usual manner asin the case of producing acrylic synthetic fibers by an ordinary andwell known wet spinning process.

According to the process of the present invention, holhow acylicsynthetic fibers can be easily obtained. Further, different from anordinary wet spinning process, the fiber is at once extruded into air orother inert gaseous medium and is then coagulated in an aqueouscoagulating bath and the filament is drawn, and therefore the spinningvelocity can be increased to be remarkably higher than in the case ofproducing synthetic fibers by a conventional wet spinning process and amore compact fiber structure can be obtained.

Examples for working the present invention are shown in the following.But the present invention is not limited to these particular examples.In the examples, the parts and percentages are all by weight.

EXAMPLE 1 A copolymer (1;) =1.4 in dimethyl formamide at C.) consistingof 91.4 parts of acrylonitrile, 8.6 parts of methyl acrylate and 0.4part of sodium allylsulfonate was dissolved in an aqueous solution ofsodium thiocyanate to prepare spinning solutions having copolymerconcentrations of 23.75 and 26.12% respectively. The viscosities at 30C. of these spinning solutions were respectively 96x10 and 125x10centipoises. Each spinning solution was heated to C., was extruded intoair through spinnerettes at a rate of 6.45 g./min. for the spinningsolution having the copolymer concentration of 23.75% and at a rate of5.86 g./min. for the spinning solution having the copolymerconcentration of 26.12%. As for the spinnerettes there were used aspinnerette having 7 spinning orifices of such shape as is shown in FIG.1 of an outside diameter of 0.605 mm., an inside diameter of 0.345 mm.and a distance d of 0.123 mm., a spinnerette having 7 spinning orificesof such shape as is shown in FIG. 2 of a short side of 0.094 mm., a longside of 0.754 mm. and a distance d of 0.230 mm. and a spinnerette having7 spinning orifices of such shape as is shown in FIG. 3 of a short sideof 0.091 mm., a long side of 0.649 mm. and a distance d of 0.200 mm. Ineach case the distance between the under surface of the spinnerette andthe surface of the solution in the coagulating bath was 0.3 cm. Theextruded spinning solution current was then passed through an aqueoussolution of 12% sodium thiocyanate kept at -3 C. Then the coagulatedfilaments were drawnat a godet speed of 41.3 m./min., then washed withwater, stretched 8 times the length in steam at 120 C., then dried for 1minute on a roller heated to C. and were heat-treated to be relaxed for4 minutes in steam at 115 C. to obtain hollow acrylic synthetic fibersof a monofilament fineness of 7 deniers. For example, microscopicphotographs of the cross-sections of hollow acrylic synthetic fibersobtained from the spinning solution of the acrylonitrile copolymerconcentration of 26.12% by using spinnerettes of shapes shown in FIGS. 1to 3 are respectively shown in FIGS. 8 to 10.

For comparison, the same acrylic polymer as was used above was dissolvedin an aqueous solution of 60% sodium thiocyanate to obtain a spinningsolution having a copolymer concentration of 11.3%. The spinningsolution was heated to 70 C. and extruded into an aqueous solution of12% sodium thiocyanate kept at 3 C.

TABLE 1 Used spinnerette Cil- Orifice shape of cular orifice Fig. 1 Fig3 Flg 2 r concentration ggi' iiiit 11. s 23. 75 20.12 26. s 26.12 Drystrength (g./d.) 3.18 3. 60 3. 90 3. s 4. 2o Knot strength (g./d.) 2.002. 30 2. 80 2. 57 2. 34 Dry elongation (perceut)- 29. 6 27. 4 29. 2 27.4 28. 0 Knot elongation (percent) 10.4 10. 9 22.0 19.1 10. 0 Luster 3048 46 45 56 In this example, the luster was measured by the followingmethod:

Luster (1) 1 g. of fibers cut to 4 to cm. long was taken and the fiberswere arranged and ironed.

(2) The arranged fibers were pasted at both ends to a cardboard by usinga binder and were then ironed.

(3) The luster of the above mentioned fibers pasted to the cardboard wasmeasured by using a Murakami MG5 luster meter (made by Murakami ColorTechnical Laboratory) As apparent from the Table 1, the hollow fibersobtained by the process of the present invention had the same yarnproperties as the fibers obtained by the ordinary wet spinning process,but had lusters better than of the solid fibers obtained by the ordinarywet spinning process.

EXAMPLE 2 The same acrylic polymer as was used in Example 1 wasdissloved in an aqueous solution of 50% sodium thiocyanate to preparespinning solutions respectively having polymer concentrations of 21.72and 17.42%. The viscosities at C. of these spinning solutions wererespectively 22.4 10 and 489x10 centipoises. Each spinning solution washeated to 70 C., and was extruded into air through a spinerette having 7spinning orifices of such shape as is shown in FIG. 2 (a short side of0.094 mm., a long side of 0.754 mm. and a distance d of 0.230 mm.) orthrough a spinnerette having 7 spinning orifices of such shape as isshown in FIG. 3 (a short side of 0.091 mm., a long side of 0.649 mm. anda distance d of 0.200 mm.). The distance between the under surface ofthe spinnerette and the surface of the solution in the coagulating bathwas 0.3 mm. The extruded solution was then passed through an aqueoussolution of 12% sodium thiocyanate kept at 3 C. The coagulated filamentswere drawn at a godet speed of m./min., then washed 'with water,stretched 8 times the length in steam at 120 C., dried for 1 minute on aroller heated to 115 C. and were heat-treated to be relaxed for 4minutes in steam at 115 C. to obtain 10 denier (monofilament denier)hollow acrylic synthetic fibers.

EXAMPLE 3 The same acrylic polymer as was used in Example 1 wasdissolved in an aqueous solution of 60% sodium thiocyanate to prepare aspinning solution having a copolymer concentration of 17%. The viscosityat 30 C. of the spinning solution was 5 .50 X 10 centipoises. Thespinning solution was heated to 70 C., and extruded into air through aspinnerette having 7 spinning orifices of such shape as is shown in FIG.1 (an outside diameter of 0.762 mm., an inside diameter of 0.502 mm., anarea of the part enclosed with the slit of 0.20 mm. and a distance d of0.123 mm.). The distance between the under surface of the spinneretteand the surface of the solution in the coagulating bath was 0.2 cm. Thenthe extruded solution was coagulated in an aqueous solution of 12%sodium thiocyanate kept at 3 C. The coagulated filaments were drawn at agodet speed of 40 m./min., washed with water, stretched 8 times thelength in steam at 120 0, dried for 1 minute on a roller heated to 115C. and were heat-treated to be relaxed for 4 minutes in steam at 115 C.to obtain 10 denier (monofilament denier) hollow acrylic syntheticfibers.

EXAMPLE 4 The same spinning solution as in Example 3 was warmed to C.,and extruded into air through a spinnerette having 7 spinning orificesof the shape shown in FIG. 1 (an outside diameter of 0.908 mm., aninside diameter of 0.702 mm., an area of the part enclosed with the slitof 0.40 mm. and a distance d of 0.146 mm.). The distance between theunder surface of the spinnerette and the surface of the solution in thecoagulating bath was 0.5 cm. Then the extruded solution was coagulatedin an aqueous solution of 12% sodium thiocyanate kept at 3 C. Thecoagulated filaments were drawn at a godet speed of 35 m./min., washedwith water, stretched 12 times the length in steam at 120 C., dried for1 minute on a roller heated to 115 C. and were heated-treated to berelaxed for 4 minutes in steam at 115 C. to obtain 10 denier(monofilament denier) hollow acrylic synthetic fibers.

EXAMPLE 5 The same acrylic polymer as was used in Example 1 wasdissolved in an aqueous solution of 60% sodium thiocyanate to prepare aspinning solution having a copolymer concentration of 25%. The viscosityat 30 C. of the spinning solution was x10 centipoises. The spinningsolution was warmed to 70 C., and extruded into air through aspinnerette having 7 spinning orifices of such shape as is shown in FIG.1 (an outside diameter of 0.464 mm., an inside diameter of 0.224, anarea of the part enclosed with the slit of 0.04 mm. and a distance d of0.100 mm.). The distance between the under surface of the spinneretteand the surface of the solution in the coagulating bath was 0.3 cm. Thenthe extruded solution was coagulated in an aqueous solution of 12%sodium thiocyanate kept at 13 C. The coagulated filaments were drawn ata godet speed of 35 m./min., washed with water, stretched 8 times thelength in steam at 120 0, dried for 1 minute on a roller heated to 11.5C. and then were heat-treated to be relaxed for 4 minutes in steam at C.to obtain 10 denier (monofilament denier) hollow acrylic syntheticfibers.

EXAMPLE 6 The same acrylic polymer as was used in Example 1 wasdissolved in an aqueous solution of 60% sodium thiocyanate to prepare aspinning solution having a copolymer concentration of 26.88%. Theviscosity at 30 C. of the spinning solution was 198x10 centipoises. Thespinning solution was warmed to 70 C. and extruded into air through aspinnerette having 7 spinning orifices of the shape shown in FIG. 1 (anoutside diameter of 0.605 mm., an inside diameter of 0.345 mm., an areaof the part enclosed with the slit of 0.09 mm. and a distance a of 0.123mm.). The distance between the under surface of the spinnerette and thesurface of the solution in the coagulating bath was 0.7 cm. Then theextruded solution was coagulated in an aqueous solution of 12% sodiumthiocyanate kept at 3 C. The coagulated filaments were drawn at a godetspeed of 50 m./min., washed with water, stretched 12 times the length insteam at C., dried for 1 minute on a roller heated to 115 C. and wereheat-treated to be relaxed for 4 minutes in steam at 115 C. to obtain 10denier (monofilament denier) hollow acrylic synthetic fibers.

What we claim is:

1. A process for producing hollow acrylic synthetic fibers whichcomprises extruding a spinning solution prepared by dissolving anacrylic polymer in a concentrated aqueous solution of an inorganic saltselected from the group consisting of sodium thiocyanate, potassiumthiocyanate, ammonium thiocyanate, calcium thiocyanate, sodiumperchlorate, calcium perchlorate, zinc chloride and lithium chloridethrough spinning orifices into an inert gaseous medium which isincapable of coagulating the spinning solution, each spinning orificehaving a continuous central portion substantially enclosed by a slithaving at least one cut-out in order that during passage through theinert gaseous medium an inert gas-filled hollow current of the spinningsolution is formed, and coagulating the hollow current by means of anaqueous coagulating bath.

2. A method as claimed in claim 1 wherein the continuous central portionof the spinning orifices has an area of at least 0.04 mm.

3. A method as claimed in claim 1 wherein the acrylic polymer ispolyacrylonitrile or a copolymer of at least 70% by weight ofacrylonitrile the balance being at least one ethylenically unsaturatedmonomer copolymerizable with acrylonitrile.

4. A method as claimed in claim 1 wherein the viscosity of the spinningsolution is in the range of from 4 10 to 4 10 centipoises.

5. A method as claimed in claim 1 wherein the distance 8 between theunder surface of the spinnerette and the surface of the solution in thecoagulating bath is from 0.2 cm. to 5.0 cm.

References Cited UNITED STATES PATENTS 2,302,555 11/1942 Klammroth264-177F 2,764,468 9/1956 Have *264-177F 3,080,210 3/1963 Ucci 264-2033,323,168 6/1967 Drunen et a1. 264-177F 3,340,571 9/1967 Bishop et a1264-177F 3,412,191 11/1968 Kitajima et a1. 264-177F 3,405,424 10/1968Imodesteg et a1. 264-177F 3,447,998 6/ 1969 Fitzgerald et a1. 161-1773,492,692 2/1970 Soda 18-8SC 3,528,128 9/1970 Murakami et a1.

FOREIGN PATENTS 356,866 10/1961 Switzerland 161-178 900,441 4/1962 GreatBritain 264-177F 695,270 9/1964 Canada 264-177F 38/9314 6/1963 Japan264-182 44/899 1/ 1969 Japan.

JAY H. WOO, Primary Examiner US. Cl. X.R.

264-182; 18-8SC, SSS; 161-177, 178

